This invention generally relates to the logging of subterranean wells. More particularly, the invention relates to the logging of such wells using a fiber optic line and fiber optic sensors.
Prior art logging systems have been deployed via electric wireline and via slickline. Wireline deployed logging systems are able to transmit the data collected by the logging tool real time through the electric line. Although wireline deployed logging systems are able to transmit data real time via the electrical wires, such systems require a grease injector in order to ensure that pressure from the wellbore does not escape around the wireline as it is inserted into a pressurized well during deployment and use. Grease injectors, however, are problematic instruments to use, since they require great care during maintenance and operation, have a tendency to leak under pressure and continual wear, and present an environmental hazard when such leaks occur. Moreover, wireline deployed logging systems are costly to deploy.
On the other hand, current slickline deployed lines are manufactured from solid wire and are not able to transmit the logging tool data real time to surface. Instead, slickline deployed logging systems use memory tools connected to the lower end of the line. In slickline memory logging, the slickline and battery-powered memory tools are lowered downhole on the end of the slickline and the memory tool is used to record the downhole logging tool data for subsequent download and collection at the surface once the tools are retrieved from the well. The advantages of slickline deployed systems are that they are much less costly and easier to deploy than wireline deployed systems, they can be run in the hole and out of the hole faster than braided wire, and they are easier to seal against well pressure at the well head.
Most of the logging tools deployed on wireline or slickline are electrically powered devices. Electrically powered devices include electronics that are very sensitive and that often become damaged in the hard environment of a subterranean wellbore. In addition, some logging tools are memory tools and/or include downhole batteries. It is often difficult to shield or protect these electrical components against the high temperatures and pressures commonly found in a wellbore, which high temperatures and pressures typically deteriorate and damage the electrical components of the tools.
Thus, there exists a continuing need for an arrangement and/or technique that addresses one or more of the problems that are stated above. In particular, the prior art would benefit from a logging system that has the capability of transmitting the logging tool data real time to surface, that is as economical and as easy to deploy as slickline deployed systems, and that does not include the detriments of electrically or battery powered devices.